"""
Creates a MobileNetV3 Model as defined in:
Andrew Howard, Mark Sandler, Grace Chu, Liang-Chieh Chen, Bo Chen, Mingxing Tan, Weijun Wang, Yukun Zhu,
Ruoming Pang, Vijay Vasudevan, Quoc V. Le, Hartwig Adam. (2019).
Searching for MobileNetV3
arXiv preprint arXiv:1905.02244.
"""
from typing import Optional, Callable
import torch.nn as nn
import math

from super_gradients.common.registry.registry import register_model
from super_gradients.common.object_names import Models
from super_gradients.training.models.classification_models.mobilenetv2 import MobileNetBase
from super_gradients.training.utils import get_param


def _make_divisible(v, divisor, min_value=None):
    """
    This function is taken from the original tf repo.
    It ensures that all layers have a channel number that is divisible by 8
    It can be seen here:
    https://github.com/tensorflow/models/blob/master/research/slim/nets/mobilenet/mobilenet.py
    """
    if min_value is None:
        min_value = divisor
    new_v = max(min_value, int(v + divisor / 2) // divisor * divisor)
    # Make sure that round down does not go down by more than 10%.
    if new_v < 0.9 * v:
        new_v += divisor
    return new_v


class h_sigmoid(nn.Module):
    def __init__(self, inplace=True):
        super(h_sigmoid, self).__init__()
        self.relu = nn.ReLU6(inplace=inplace)

    def forward(self, x):
        return self.relu(x + 3) / 6


class h_swish(nn.Module):
    def __init__(self, inplace=True):
        super(h_swish, self).__init__()
        self.sigmoid = h_sigmoid(inplace=inplace)

    def forward(self, x):
        return x * self.sigmoid(x)


class SELayer(nn.Module):
    def __init__(self, channel, reduction=4):
        super(SELayer, self).__init__()
        self.avg_pool = nn.AdaptiveAvgPool2d(1)
        self.fc = nn.Sequential(
            nn.Linear(channel, _make_divisible(channel // reduction, 8)),
            nn.ReLU(inplace=True),
            nn.Linear(_make_divisible(channel // reduction, 8), channel),
            h_sigmoid(),
        )

    def forward(self, x):
        b, c, _, _ = x.size()
        y = self.avg_pool(x).view(b, c)
        y = self.fc(y).view(b, c, 1, 1)
        return x * y


def conv_3x3_bn(inp, oup, stride):
    return nn.Sequential(nn.Conv2d(inp, oup, 3, stride, 1, bias=False), nn.BatchNorm2d(oup), h_swish())


def conv_1x1_bn(inp, oup):
    return nn.Sequential(nn.Conv2d(inp, oup, 1, 1, 0, bias=False), nn.BatchNorm2d(oup), h_swish())


class InvertedResidual(nn.Module):
    def __init__(self, inp, hidden_dim, oup, kernel_size, stride, use_se, use_hs):
        super(InvertedResidual, self).__init__()
        assert stride in [1, 2]

        self.identity = stride == 1 and inp == oup

        if inp == hidden_dim:
            self.conv = nn.Sequential(
                # dw
                nn.Conv2d(hidden_dim, hidden_dim, kernel_size, stride, (kernel_size - 1) // 2, groups=hidden_dim, bias=False),
                nn.BatchNorm2d(hidden_dim),
                h_swish() if use_hs else nn.ReLU(inplace=True),
                # Squeeze-and-Excite
                SELayer(hidden_dim) if use_se else nn.Identity(),
                # pw-linear
                nn.Conv2d(hidden_dim, oup, 1, 1, 0, bias=False),
                nn.BatchNorm2d(oup),
            )
        else:
            self.conv = nn.Sequential(
                # pw
                nn.Conv2d(inp, hidden_dim, 1, 1, 0, bias=False),
                nn.BatchNorm2d(hidden_dim),
                h_swish() if use_hs else nn.ReLU(inplace=True),
                # dw
                nn.Conv2d(hidden_dim, hidden_dim, kernel_size, stride, (kernel_size - 1) // 2, groups=hidden_dim, bias=False),
                nn.BatchNorm2d(hidden_dim),
                # Squeeze-and-Excite
                SELayer(hidden_dim) if use_se else nn.Identity(),
                h_swish() if use_hs else nn.ReLU(inplace=True),
                # pw-linear
                nn.Conv2d(hidden_dim, oup, 1, 1, 0, bias=False),
                nn.BatchNorm2d(oup),
            )

    def forward(self, x):
        if self.identity:
            return x + self.conv(x)
        else:
            return self.conv(x)


class MobileNetV3(MobileNetBase):
    def __init__(self, cfgs, mode, num_classes=1000, width_mult=1.0, in_channels: int = 3):
        super(MobileNetV3, self).__init__()
        # setting of inverted residual blocks
        self.cfgs = cfgs
        assert mode in ["large", "small"]

        # building first layer
        curr_channels = _make_divisible(16 * width_mult, 8)
        layers = [conv_3x3_bn(in_channels, curr_channels, 2)]
        # building inverted residual blocks
        block = InvertedResidual
        for k, t, c, use_se, use_hs, s in self.cfgs:
            output_channel = _make_divisible(c * width_mult, 8)
            exp_size = _make_divisible(curr_channels * t, 8)
            layers.append(block(curr_channels, exp_size, output_channel, k, s, use_se, use_hs))
            curr_channels = output_channel
        self.features = nn.Sequential(*layers)
        # building last several layers
        self.conv = conv_1x1_bn(curr_channels, exp_size)
        self.avgpool = nn.AdaptiveAvgPool2d((1, 1))
        output_channel = {"large": 1280, "small": 1024}
        output_channel = _make_divisible(output_channel[mode] * width_mult, 8) if width_mult > 1.0 else output_channel[mode]
        self.classifier = nn.Sequential(
            nn.Linear(exp_size, output_channel),
            h_swish(),
            nn.Dropout(0.2),
            nn.Linear(output_channel, num_classes),
        )

        self._initialize_weights()

    def forward(self, x):
        x = self.features(x)
        x = self.conv(x)
        x = self.avgpool(x)
        x = x.view(x.size(0), -1)
        x = self.classifier(x)
        return x

    def _initialize_weights(self):
        for m in self.modules():
            if isinstance(m, nn.Conv2d):
                n = m.kernel_size[0] * m.kernel_size[1] * m.out_channels
                m.weight.data.normal_(0, math.sqrt(2.0 / n))
                if m.bias is not None:
                    m.bias.data.zero_()
            elif isinstance(m, nn.BatchNorm2d):
                m.weight.data.fill_(1)
                m.bias.data.zero_()
            elif isinstance(m, nn.Linear):
                n = m.weight.size(1)
                m.weight.data.normal_(0, 0.01)
                m.bias.data.zero_()

    def replace_input_channels(self, in_channels: int, compute_new_weights_fn: Optional[Callable[[nn.Module, int], nn.Module]] = None):
        from super_gradients.modules.weight_replacement_utils import replace_conv2d_input_channels

        self.features[0][0] = replace_conv2d_input_channels(conv=self.features[0][0], in_channels=in_channels, fn=compute_new_weights_fn)

    def get_input_channels(self) -> int:
        return self.features[0][0].in_channels


@register_model(Models.MOBILENET_V3_LARGE)
class mobilenetv3_large(MobileNetV3):
    """
    Constructs a MobileNetV3-Large model
    """

    def __init__(self, arch_params):
        width_mult = arch_params.width_mult if hasattr(arch_params, "width_mult") else 1.0
        cfgs = [
            # k, t, c, SE, HS, s
            [3, 1, 16, 0, 0, 1],
            [3, 4, 24, 0, 0, 2],
            [3, 3, 24, 0, 0, 1],
            [5, 3, 40, 1, 0, 2],
            [5, 3, 40, 1, 0, 1],
            [5, 3, 40, 1, 0, 1],
            [3, 6, 80, 0, 1, 2],
            [3, 2.5, 80, 0, 1, 1],
            [3, 2.3, 80, 0, 1, 1],
            [3, 2.3, 80, 0, 1, 1],
            [3, 6, 112, 1, 1, 1],
            [3, 6, 112, 1, 1, 1],
            [5, 6, 160, 1, 1, 2],
            [5, 6, 160, 1, 1, 1],
            [5, 6, 160, 1, 1, 1],
        ]
        super().__init__(cfgs, mode="large", num_classes=arch_params.num_classes, width_mult=width_mult, in_channels=get_param(arch_params, "in_channels", 3))


@register_model(Models.MOBILENET_V3_SMALL)
class mobilenetv3_small(MobileNetV3):
    """
    Constructs a MobileNetV3-Small model
    """

    def __init__(self, arch_params):
        width_mult = arch_params.width_mult if hasattr(arch_params, "width_mult") else 1.0
        cfgs = [
            # k, t, c, SE, HS, s
            [3, 1, 16, 1, 0, 2],
            [3, 4.5, 24, 0, 0, 2],
            [3, 3.67, 24, 0, 0, 1],
            [5, 4, 40, 1, 1, 2],
            [5, 6, 40, 1, 1, 1],
            [5, 6, 40, 1, 1, 1],
            [5, 3, 48, 1, 1, 1],
            [5, 3, 48, 1, 1, 1],
            [5, 6, 96, 1, 1, 2],
            [5, 6, 96, 1, 1, 1],
            [5, 6, 96, 1, 1, 1],
        ]
        super().__init__(cfgs, mode="small", num_classes=arch_params.num_classes, width_mult=width_mult, in_channels=get_param(arch_params, "in_channels", 3))


@register_model(Models.MOBILENET_V3_CUSTOM)
class mobilenetv3_custom(MobileNetV3):
    """
    Constructs a MobileNetV3-Customized model
    """

    def __init__(self, arch_params):
        super().__init__(
            cfgs=arch_params.structure,
            mode=arch_params.mode,
            num_classes=arch_params.num_classes,
            width_mult=arch_params.width_mult,
            in_channels=get_param(arch_params, "in_channels", 3),
        )
